Do you use C++? C#? Or managed Directx? And what kind of concepts are you talking about?

Please give us some more information as this is too little to go after...

Either way, in my experience the key is never to give up . So if you don't know some functions, don't be scared, just try to figure out what they do, you could google it.

Do you understand, in the case of swap chains, how they work? And just don't know how to use them?

I'm just trying to understand your question...

This tutorial covers some of the basics:

http://directxtutorial.com/Lesson.aspx?lessonid=11-4-1

And then how to use some of them:

http://directxtutorial.com/Lesson.aspx?lessonid=11-4-2

You don't NEED to remember ALL functions...

Now I'm not in the real industry yet, so this is just my personal opinion, but I don't remember all functions, just the nessesary, and some times I Google them if nessesary. But either way, you will start remembering the functions after a while of using Directx.